This invention relates to a portable electrostatic spray device designed for personal use. More particular, this invention is focused on providing improvements to both the electronic circuit and mechanical designs which lead to the reduction/elimination of shock potentials, thereby improving the safety of the device for the user.
In U.S. Pat. No. 4,549,243, Owen describes a spraying apparatus that can be held in the human hand for applications such as graphic work where it is desired that the area to which the spray is applied can be precisely controlled (Col 1, 11 5-9). Owen acknowledges both the benefits and hazards associated with stored capacitance when he describes that the high voltage circuit has sufficient capacitance that, during use, the desired electrical gradient at the nozzle is maintained between pulses but on the other hand should have a low stored energy, preferably less 10 mJ, so that no safety hazard is presented to the user for example by accidental contact of the user with the nozzle or on contact of the nozzle with an earthed surface (Col 5, 11 52-59). Owen further describes the occurrence of spark discharges and offers a solution to reduce such discharges, xe2x80x9c. . . when a nozzle with a high potential applied thereto is brought close to an earthed surface, spark discharges from the nozzle to the earthed surface may occur instead of spraying; it is preferred that the field strength at the nozzle is such that the maximum distance of the nozzle from an earthed surface at which spark discharges occur is less than 5 mmxe2x80x9d (Col 6, 11 14-20). Although recognizing the dangers associated with stored capacitance within the device, Owen fails to offer a means of dissipating said capacitance and chooses to try to design around it. The approach of designing around the internal capacitance, limiting to 10 mJ or less, limits the size/quantity of capacitors within the circuitry which in turn limits the ability to hold the output high voltage at a steady value. Further, Owen""s electrical gradient design of limiting the distance at which a spark discharge will occur is not a consumer viable solution as it is very likely that a consumer will come in direct contact with the nozzle area (i.e. less than the 5 mm distance) either while the device is in operation or shortly thereafter before stored charge has been dissipated from the device.
In U.S. Pat. No. 5,222,664, Noakes provides an electrostatic spraying device with the added benefit of a shock suppression by means of high voltage circuitry having a bi-polar output with a frequency no greater than 10 Hz. The system described by Noakes uses an alternating polarity power supply for generation of a high voltage potential. Noakes recognizes for example, where a direct current electrostatic spraying device which is wholly hand held is used (and hence where no other path to ground exists other than through the operator), and if the operator is or becomes substantially isolated from ground (for instance, as a result of standing on a synthetic fiber carpet or wearing shoes having soles of insulating material), during spraying, charge will accumulate on the operator and, if the operator subsequently touches a grounded conductor, he/she will experience an electrical shock (Col 1, 11 46-56). Owen offers a solution for such problem by thus appropriate selection of the frequency (of the high voltage power supply switching between opposite polarities), it is possible to eliminate the sensation of electrical shock by the operator or at least reduce the sensation to a level at which the risk of an accident as a result of an involuntary reaction by the operator is reduced (Col 2, 11 26-30). However, the solution that Noakes sets forth as a means to reduce the potential for the user to build-up a charge and subsequently discharge this charge in the form of a shock is to provide specifications for the switching frequency of the alternating polarity power supply. While this may represent a viable solution for some cases, this does not find application in electrostatic spraying devices that generate high voltage power using a rectifier which use a single polarity output.
In U.S. Pat. No. 5,337,963, Noakes provides for an electrostatic spray device for the spraying of liquids and is particularly concerned with devices for spraying liquids into the surroundings. One aspect of the device set forth by Noakes is that when the cartridge is in place in the compartment and is connected to the high voltage output of the generator, the fact that the voltage is applied through the liquid column in the narrow bore of the tube will provide a high resistance path (and hence suppression of shock that would otherwise be experienced by touching the tip of the tube) by virtue of the resistivity of the liquid and the cross-section and length dimensions of the tube bore (Col 10, 11 22-30). This design, while offering some means of shock suppression, is not a consumer viable system in that it ignores the scenario where the column of liquid between the charging location and the discharge point is no longer filled with product, and therefore no longer offering a resistive path. This is the likely scenario where a user would receive a shock from such a device.
An electrostatic spraying device which is configured and disposed to electrostatically charge and dispense a product from a supply to a point of dispersal. The electrostatic spraying device has a reservoir configured to contain the supply of product and a nozzle to disperse the product. The nozzle being disposed at the point of dispersal. The nozzle has an exit orifice. A channel is disposed between the reservoir and the nozzle, wherein the channel permits the electrostatic charging of the product upon the product moving within the channel. A positive displacement mechanism is used to move the product from the reservoir to the nozzle. A power source supplies an electrical charge. A high voltage power supply, high voltage contact, and high voltage electrode are used. A portion of the high voltage electrode being disposed between the reservoir and the nozzle is used to electrostatically charge the product within the channel at a charging location. A distance between the charging location and the nozzle exit orifice is governed by the following relationship: Vo/d less than 100,000, wherein Vo=an output voltage of said high voltage power supply and d=linear distance between the charging location and said nozzle exit orifice. A moveable electrode cover may be used to substantially conceal the high voltage contact when the disposable cartridge is removed from the device. The high voltage contact may recess when the disposable cartridge is removed from the device or resurface when the disposable cartidge is inserted into the device.